Thinking about the most simple queueing implementation...

normal.js

var process = function (a, b) {
  // do some async stuff with a and b
};

process(foo1, bar1);
process(foo2, bar2);

queueified.js

var queue = [];

var processNext = function () {
  var a = queue[0][0],
      b = queue[0][1];

  // do some async stuff with a and b

  queue.shift();
  if (queue.length > 0)
    process.nextTick(processNext);
};

var prepare = function () {
  queue.push(arguments);
  if (queue.length === 1)
    process.nextTick(processNext);
};

prepare(foo1, bar1);
prepare(foo2, bar2);